A level of a reductant stored in a reductant tank decreases as the reductant is used, thereby requiring the reductant tank to be refilled. U.S. Published Application No. 2011/0209465 relates to a liquid additive reservoir including a rigid casing delimiting a housing, and a fluid-tight flexible pouch mounted inside the housing of the casing and intended to contain the liquid additive, the flexible pouch being designed to be connected to the exhaust line of an internal combustion engine of a vehicle.